This may look like a normal robot lawnmower, the sort that trundles mindlessly around suburban lawns all over the country, but OpenMower is more than that, thanks to the clever use of two Raspberry Pi boards. The brainchild of German tech entrepreneur Clemens Elflein, and reported on by Hackster, OpenMower upgrades the internals of a standard robot mower to make it smarter using a Raspberry Pi 4, and the $4 Raspberry Pi Pico.
Little more than weaponized robot vacuum cleaners, most robot mowers operate using a perimeter wire that they may not cross. They stay inside the area defined by the wire, and if they run into something, or otherwise detect an obstacle in their path, they will randomly change direction and head off until they encounter another obstacle or wire. This way, they cut all the grass, but can produce a random pattern and potentially an uneven cut.
To fix this, Elflein took apart an off-the shelf robot lawnmower. He discovered that it used standard connectors to fit together, so kept the shell, motors, chassis, and blade, but gave it a heavy electronics upgrade in the form of a Raspberry Pi 4, Raspberry Pi Pico, custom speed control system, and an Ardusimple RTK (real time kinematics) GPS board. The RTK GPS board provides both coarse GPS location data, along with a correction stream (RTK) which sharpens the accuracy from meters to centimeters.
This last component is crucial, as it allows the OpenMower to do away with the clunky perimeter wire and know precisely where it is within the lawn, supporting multiple mowing areas and moving back and forth in a regular pattern instead of randomly turning. It still will have the ability to avoid obstacles, as the Raspberry Pi Pico acts as the low level controller, interfacing with sensors and reporting back to the Raspberry Pi 4.
The OpenMower is still a work in progress, with a list of features yet to be implemented including the object avoidance system and a phone app. Currently, an Xbox controller is used to drive the mower around manually to set the boundary of the mowing area, with circles driven around immovable objects such as trees to mark exclusion zones. The Pi 4 uses RTK data from the internet and combines it with the feed from its own GPS module to calculate its precise position, and uses custom software to plan an efficient mowing route through the defined area that leaves a nice pattern behind.